WASHINGTON -- Lawyers for Sen. Larry Craig asked a Minnesota appeals court Tuesday to allow him to withdraw his guilty plea stemming from his June arrest in a public bathroom sex sting, citing a "grave procedural flaw."

Larry Craig, pictured here in August, says it's unjust not to be given another chance to prove he's innocent.

The Idaho Republican argues that a state law related to his misdemeanor conviction is unconstitutional and that it's "manifestly unjust" not to allow him to be given another chance to prove his innocence.

A state judge refused on October 4 to allow the senator to withdraw his earlier plea. Judge Charles Porter ruled the plea "was accurate, voluntary and intelligent, and ... supported by the evidence."

Craig had earlier promised to resign if the judge ruled against his motion, but he changed his mind and vowed to stay in office until his term expires in early 2009. He is not seeking re-election this year.

Craig, 62, also faces a Senate ethics committee investigation of his actions after his arrest by an undercover officer in a public restroom at Minneapolis International Airport in Minnesota.

He pleaded guilty in writing in August to a misdemeanor disorderly conduct charge, and a soliciting charge was dropped. He has since denied the charges.

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Led by Washington attorney William Martin, Craig's legal team claimed in its newest brief that "the plea was not supported by the evidence" and "was defective because it was not accepted by the sentencing judge."

"The only interpretation that the government has offered of [Craig's] alleged conduct is that it was intended to communicate a desire to engage in disorderly conduct -- rather than that he engaged in any disorderly conduct," the legal brief said.

"Our brief contains legal arguments supporting Senator Craig's position that the district court abused its discretion by refusing to allow him to withdraw his guilty plea," Martin said in a written statement. "Pursuant to Minnesota law, there is an insufficient factual basis to support the finding that he is guilty of violating any laws while passing through the Minneapolis airport."

The officer claimed the senator made foot-tapping signals and other gestures to indicate his desire for illicit sexual acts while the two were sitting in adjacent restroom stalls.

Minnesota officials have 45 days to respond to the filing, Martin said. An as-yet unscheduled hearing by the Minnesota Court of Appeals would be the next legal step.

"Throughout this trying time, Senator Craig has maintained his innocence and has remained a dedicated public servant who continues to serve the people of Idaho with honor and distinction, as he has done for the past 27 years," Martin said in his statement.

In an interview in November with Boise, Idaho, TV station KTVB, Craig said, "We don't know what the appellate court will say to me. Honestly, the appeals courts tend to defend the courts below them.

"It is my right to do what I'm doing. I've already provided for Idaho [the] certainty that Idaho needed, I'm not running for re-election. I'm no longer in the way. I am pursuing my constitutional rights."

The state appeals court has not said when it will hold oral arguments, but Craig's attorneys have so far made no request for an expedited hearing, meaning the case may not be heard for months. The court will not retry the case, but only focus on whether the state trial judge made legal errors.

Three of the court's 16 judges will either sit for arguments or review the facts of the case in private. They then will have 90 days to make a ruling.

Depending on the outcome of the latest appeals, the Minnesota Supreme Court then will have the option of accepting or rejecting any further consideration of the case.

The state's highest court, which could eventually be the final arbiter of the case, accepts only about 5 percent of appeals for further review, according to court officials.

A campaign finance report filed in November with the Senate shows Craig spent about $23,000 in campaign money on lawyers in his ethics investigation. The report did not indicate money spent from his campaign coffers on his criminal defense, but Craig spokesman Dan Whiting told CNN at the time that the three-term Republican would use that money on various aspects of his criminal defense.

Campaign finance laws generally ban using such funds on items not directly related to one's official duties as an officeholder or candidate, but Whiting said the senator's spending was legal.

Larry Noble, former general counsel for the FEC, disagreed to some extent, but noted that "it's pretty clear he can use his campaign funds for his defense in the ethics committee probe since it is related to his being an officeholder."E-mail to a friend